Species: Greenland shark (Somniosus microcephalus)
Habitat: deep in the North Atlantic and the cold surface waters of the Arctic

Fish that were alive during the Age of Enlightenment are still swimming strong. A Greenland shark has lived at least 272 years, making the species the longest-lived vertebrate in the world – smashing the previous record held by a 211-year-old bowhead whale. But it may have been as old as 500 years.

“We definitely expected the sharks to be old, but we didn’t expect that it would be the longest-living vertebrate animal,” says Julius Nielsen of the University of Copenhagen, Denmark.

Living deep in the North Atlantic and the frigid surface waters of the Arctic, Greenland sharks have a stable environment and grow just a few centimetres per year. Despite their slow growth, though, they reach more than 5 metres in length and are often the apex predator in their ecosystem.

Old blue eyes
It was once thought to be impossible to age Greenland sharks. Their skeletons, made of cartilage, lack the calcified growth rings of hard-boned vertebrates. And other fish are aged by measuring calcareous bodies that grow in their ears, but this doesn’t work for sharks.

Instead Nielsen and his colleagues focused on radiation in the sharks’ eyes. Nuclear bomb tests in the 1950s and ’60s blasted radioactive particles into the atmosphere.

Those particles entered food webs all over the world and show up in the form of radioactive forms of carbon in organisms that lived through that period. Because Greenland sharks’ eye lens tissue doesn’t change during its lifetime, it preserves the historic radiation.

After catching a 2.2-metre shark that showed radiation levels indicating it was born in the 1960s and was about 50 years old, the team calculated how fast the sharks grew.

New Scientist.